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Friday, December 9, 2016

I'm not crazy about chips, but I've come to like the LM386. It is not really a little black mystery box -- as the article points out, the internal circuitry is simple and completely understandable. So you shouldn't feel any appliance-op angst when you use one of these.

Wednesday, December 7, 2016

In the BITX20 yahoo group, Farhan responded to a question about the BFO and the crystal filter in the BITX 40 Modules. In his response we learn more about the work of the members of the women's collective. Uma is the name of the lady who has the job of sorting the crystals. She sorts 1000 a day:

Farhan writes:

There is a longer explanation to this. The crystals we use in the BITX are microprocessor grade. This means that they are not very precise. Uma is the crystal sorter. She takes a bunch of 1000 crystals a day and sorts them by their frequency into different bags. Each board takes its five crystals from any one bag. Hence, the central frequency of each board will be slightly different from another board.

The central frequency of the ladder filter moves down from the oscillating frequency of the same crystal. That is why, in a set of matched crystals, one can be directly used as the carrier/beat frequency oscillator without needing any trimmer : it directly sits on the higher side skirt of the filter.

The BITX40 board's BFO usually ranges from 11.990.0 to 11.997.0, though in almost all cases it is very close to 11.998.0. The best way to determine the BFO frequency is to take it another ham's shack, tune in the BFO to zero beat on USB or LSB and note the frequency. I use the Rigol scope's built-in frequency counter to measure it off the modulator transformer's primary.

So, the IF offset should ideally set to the measured BFO's frequency. These are however, very subjective choices. Given that 2.2 KHz is not an ideal passband, 3 KHz is more like it, setting the BFO will determine how you would like to hear the receiver. Setting it close to the passband will make it bassy, setting it away will make it tinny. Setting it a few hundred hertz away will make it hollow. You get to choose which way you want to make your radio sound bad (harr! harr!)

Sunday, December 4, 2016

The "al fresco" phase has ended for my HRO receiver project. As has happened with homebrew projects around the world, this rig was literally pushed aside on the workbench to make room for BITX-40 Module Mania. I began to worry that the circuitry of the HRO receiver might suffer damage from the various kinds of electronic construction mayhem that take place on our workbenches. Also, I wanted to see what it would look like in the nice big metal box that Tim Sutton had sent me (thanks again Tim.) And I was hoping that the box would help with the AM broadcast breakthrough that I sometimes hear with this receiver. So, as you can see, I have good excuses for declaring Basta! on the HRO Al Fresco. I think it looks great. Black on silver is very cool. It sounds great. I'm listening to 40 right now. Thanks to Armand WA1UQO for the very cool HRO dial that got this all started.

Saturday, December 3, 2016

I was flying solo last night. Everyone else in the house was out. So I turned to ham radio for some company. And I was rewarded.

I called CQ with my BITX DIGI-TIA rig and was immediately answered by Doc AC7M in far-off Twin Peaks, Idaho. Doc was running a K3 to a homebrew solid state full gallon amp. And get this -- Doc had also homebrewed the 3 kw switching power supply. I looked at my store-bought supply and felt like an appliance operator. I hang my head in shame.

As we discussed solid state amplifiers, we were joined by another builder of silicon after-burners: Don K9AQ, who called in from a beautiful cabin in rural Wisconsin. Don's amp is based on the venerable EB-104 design. Both Don and Doc talked about the work of W6PQL. He has a really amazing site devoted to homebrew solid stat amps, and he is selling lots of great boards and parts for this kind of project: http://www.w6pql.com/As I finishing up with Don and Doc, I got a very welcome call from an old friend from the SolderSmoke community: Dino KL0S. He as booming in from Williamsburg, Va. Dino has an amazing workshop. He is building a serious vertical antenna for 160 meters. Dino is going for the DX.

Dino's Bench

At this point Mike WA3O in Pittsburgh called in. And get this: Mike heard me on his new BITX 40 Module. The Radio Gods Have Spoken! (TRGHS!). We switched up to 7.285 MHz where I fired up my BITX 40 Module for a BITX40-BITX40 QSO (albeit not at QRP levels). We should definitely make more use of 7.285 for BITX40 and other HB QRP SSB QSOs. 1930 EST (0030 Z) seems like a good time.

Finally, just when I was thinking that things couldn't get any better, they did: Armand WA1UQO called in from Richmond. Armand and I collaborate on parts acquisition at Virginia hamfests. We specialize in the contents of the musty cardboard boxes found under the tables. We discussed the DISRUPTIVE influence of Farhan's BITX 40: All around the world, other homebrew projects are being literally pushed aside on workbenches to make room for that fantastic little module from Hyderabad.I was very pleased to hear that Armand is building an analog VFO for his module, using a coil in the 4 uH range, wound on a piece of cardboard tube from a coathanger. The inspiration for this kind of coil (which I now have in THREE rigs) came from Farhan, who used sipping straws from fast-food restaurants as coil forms in a sig generator that he built years ago. This week, seeing a Facebook picture of my daughter and me in a restaurant with drinking glasses in front of us, Farhan asked if I had brought home the straws.

Thursday, December 1, 2016

We've talked many times about the pleasures associated with a rig that is still just a collection of parts and boards, all still spread out on the workbench, unboxed, perhaps held together by clip leads and bits of duct tape. They seem to sound better this way. This is the condition under which we experience that magical moment of "First Signals" (similar to First Light with a new telescope). We haven't had a concise way of describing this (note my long-winded description above). Well, this morning the Sage of Newbury Park has, on his amazing blog, provided us with the words that we have so long needed:

Al Fresco!

That's it! Perfect. When a new rig is put into operation in this way, we will henceforth say that it is being run "al fresco." Thanks Pete!

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